1. Field of Invention
The present invention relates in general to the field of corrosion protection for metal conductors used in electronic devices. More particularly, the present invention relates to real-time, early warning detection of corrosive gases, especially elemental sulfur (S8), in air based on a change in the fluorescence intensity of a substrate that includes a polymer-bound phosphine compound having sulfur-getting functionality.
2. Background Art
Acid-bearing gases in air (e.g., the air within a data center) can lead to a greater incidence of corrosion-induced hardware failures in computer systems and other electronic devices. This problem is especially prone to occur in industrialized countries. Sulfur components (e.g., elemental sulfur, hydrogen sulfide, and/or sulfur oxides) in the air are particularly troublesome gases. It has been demonstrated that the most aggressive of these sulfur-bearing gases is elemental sulfur (S8).
Corrosion of metal conductors caused by sulfur components in the air is especially severe when one or more of the metal conductors is/are a silver-containing metal. Such silver-containing metal conductors are frequently used in electronic devices to electrically connect electronic components. Examples include the silver layer of gate resistors, described below, and many lead-free solders (e.g., Sn—Ag—Cu solder).
A data center is a facility used to house numerous computer systems and various associated systems, such as data storage systems and telecommunications systems. Data centers typically include redundant/backup power supplies, redundant data communications connections, environmental controls (e.g., HVAC, fire suppression, and the like) and security systems. Data centers are also known as “server farms” due to the large number of computer systems (e.g., servers) typically housed within these facilities.
Typically, the environment of a data center is not monitored for the specific nature of gaseous components. This leaves two options: 1) assume that the data center is relatively clean (i.e., the data center environment is MFG Class I or MFG Class II); or 2) harden the electronic components of the computer systems and the various associated systems housed in the data center. The former option (option 1) leaves at risk the computer systems and the various associated systems housed within the data center. The latter option (option 2) drives additional cost (via the purchase of hardened components or use of conformal coatings which provide some level of protection).
With regard to hardening solutions, it is known to cover metal conductors with a conformal coating to protect the metal conductors from corrosion. For example, U.S. Pat. No. 6,972,249 B2, entitled “Use of Nitrides for Flip-Chip Encapsulation”, issued Dec. 6, 2005 to Akram et al., discloses a semiconductor flip-chip that is sealed with a silicon nitride layer on an active surface of the flip-chip. U.S. patent application Ser. No. 12/696,328, entitled “Anti-Corrosion Conformal Coating for Metal Conductors Electrically Connecting an Electronic Component”, filed Jan. 29, 2010 by Boday et al., discloses a conformal coating that comprises a polymer into which a phosphine compound is impregnated and/or covalently bonded. The phosphine compound in the polymer reacts with any corrosion inducing sulfur component in the air and prevents the sulfur component from reacting with the underlying metal conductors. However, as mentioned above, a key disadvantage with such hardening solutions is cost.
As mentioned above, the problem of corrosion caused by sulfur components (e.g., elemental sulfur, hydrogen sulfide, and/or sulfur oxides) in the air is especially severe when one or more of the metal conductors that electrically connect an electronic component is/are a silver-containing metal. For example, each of the gate resistors of a resistor network array typically utilizes a silver layer at each of the gate resistor's terminations. Gate resistors are also referred to as “chip resistors” or “silver chip resistors”. Typically, gate resistors are coated with a glass over coat for corrosion protection. Also for corrosion protection, it is known to encapsulate gate resistors in a resistor network array by applying a coating of a conventional room temperature-vulcanizable (RTV) silicone rubber composition over the entire printed circuit board on which the resistor network array is mounted. However, the glass over coat and conventional RTV silicone rubber compositions fail to prevent or retard sulfur components in the air from reaching the silver layer in gate resistors. Hence, any sulfur components in the air will react with the silver layer in the gate resistor to form silver sulfide. This silver sulfide formation often causes the gate resistor to fail, i.e., the formation of silver sulfide, which is electrically non-conductive, produces an electrical open at one or more of the gate resistor's terminations.
FIG. 1 illustrates, in an exploded view, an example of a conventional gate resistor 100 of a resistor network array. A resistor element 102 is mounted to a substrate 104, such as a ceramic substrate. The gate resistor 100 includes two termination structures 110, each typically comprising an inner Ag (silver) layer 112, a protective Ni (nickel) barrier layer 114, and an outer solder termination layer 116. Typically, for corrosion protection, the gate resistor 100 is coated with a glass over coat 120. Additionally, for corrosion protection, a coating (not shown) of a conventional RTV silicone rubber composition may encapsulate the gate resistor 100. As noted above, it is known to encapsulate gate resistors in a resistor network array mounted on a printed circuit board by applying a coating of a conventional RTV silicone rubber composition over the entire board. However, as noted above, the glass over coat 120 and conventional RTV silicone rubber compositions fail to prevent or retard sulfur components in the air from reaching the inner silver layer 112. Hence, any sulfur components in the air will react with the inner silver layer 112 to form silver sulfide 202 (shown in FIG. 2). FIG. 2 illustrates, in a sectional view, the conventional gate resistor 100 shown in FIG. 1, but which has failed due to exposure to sulfur-bearing gases. The silver sulfide formation 202 (often referred to as silver sulfide “whiskers”) produces an electrical open at one or more of the gate resistor's terminations 110 because silver sulfide is an electrical non-conductor and, thereby, results in failure of the gate resistor 100.
The use of silver as an electrical conductor for electrically connecting electronic components is increasing because silver has the highest electrical conductivity of all metals, even higher than copper. In addition, the concentration of sulfur components in the air is unfortunately increasing as well. Hence, the problem of corrosion caused by sulfur components in the air is expected to grow with the increased use of silver as an electrical conductor for electrically connecting electronic components and the increased concentration of sulfur components in the air.
Traditional mechanisms for monitoring data center corrosive gas concentration have focused on copper (Cu) and silver (Ag) corrosion coupons strategically placed throughout the data center. Both Cu and Ag corrosion coupons react with the corrosive gases and provide a warning either through a visual indication of gas-induced corrosion on the coupon itself or through monitoring the coupon for a change in resistance. However, both of these approaches require significant corrosion of the coupon metallurgy to have occurred before warning is provided. Unfortunately, by the time either of these approaches provides a warning that gas-induced corrosion has occurred with respect to the corrosion coupon, unprotected computer hardware housed in the data center will have already experienced corrosion damage.
Monitors exist for detecting the presence of sulfur oxides and/or hydrogen sulfide in air, but no monitors exist that provide an early warning detection of the presence of elemental sulfur in air.
Therefore, a need exists for an enhanced mechanism for monitoring the air in data centers and other facilities housing computer systems to provide an early warning detection of the presence of corrosive gases, especially elemental sulfur (S8), so that appropriate mitigation can be undertaken.